It is often required for components to be individually identified as they pass through a series of manufacturing stages so that a history of their manufacture is available for reference. One known method of identification is disclosed in our U.K. Patent No. 2201808.
These components or workpieces are conveniently provided with a dot matrix code identification marking and the dot matrix code is read using an optical reader. The dot matrix code marking comprises a plurality of rows and columns on which dots comprising the code marking are located. The reader produces an output which is converted into a digital form by a processor. A further processor is provided to determine the orientation and position of the dot matrix code from the digitised image. The further processor works by calculating the outer borders of the dot matrix code from the individual dots in the digitised image. This means that the edge of the dot matrix code has to have a reasonable number of dots along it and each dot must be accurately located. However, not all dot matrix codes meet these requirements because the edges of some dot matrix codes have very few dots and in some cases the image processing performed to locate the dots is insufficient to locate all the dots. Our U.K. Patent Application No. 9405337.8 describes a method and apparatus for identifying the orientation of a dot matrix code marking of an article. However, there still remains the problem of reading a code that has been partly obscured or damaged during processing of the article.